In the past, one generally employed technique for mounting discrete electrical components to circuit boards involved the insertion of lead ends of the components through apertures in the boards and then soldering the inserted ends to contact pads about such apertures. Another mounting technique involves the use of a template for locating and holding the components to be assembled. The template is typically placed over a substrate to which components are to be assembled. The template has apertures of the size and shape of the components in predetermined positions which correspond to underlying contact pads for the components. A solder paste is preapplied to the contact pads. The leads of the components are foreshortened and bent downward such that the ends of the leads are pushed into contact with the solder paste when the components rest on the surface of the substrate between such contact pads. The assemblage of the substrate and the components, held in place by the template, is now placed into a solder reflow oven and heated to the melting temperature of the solder in the paste to cause the solder to reflow. After the assemblage has passed through the oven and the solder has resolidified, the components have become permanently mounted to the substrate. While the solder remains liquid, the components are retained in their respective positions by the template.
The assembly of electrical components by the latter technique results in occasional mounting defects. It has been observed that defects tend to occur when components become reoriented during their placement into the respective apertures of the template. As a result of such reorientation, circuit terminations of the leads apparently fail to make sufficient contact with the solder paste on the contact pads. Thus, during the reflowing of the solder, electrical and mechanical contact may break between the contact pad on the substrate and the circuit termination of the affected lead.